1. Field of the Invention
The present invention relates to an air conditioning apparatus capable of conducting a heating operation using a refrigerating cycle which is suitable, in particular, for an electric car.
2. Description of Related Art
A technique for heating air using a refrigerant compressor operated by an electric motor is known in the art. In this technique, the compressor is located in a refrigerating circuit which, in addition to the compressor, includes an inside heat exchanger as a condenser connected to the compressor for receiving a high temperature refrigerant, a pressure reduction device for reducing a pressure of the refrigerant from the inner heat exchanger, and an outside heat exchanger acting as an evaporator for receiving the pressure reduced refrigerant from the pressure reduction device and for returning the refrigerant to the compressor. The inner heat exchanger acting as a condenser is located in an air duct in which an air flow is created and discharged to the interior of the vehicle. At the inner heat exchanger, a heat exchange takes place between the air in the duct and the high temperature refrigerant, so that the air is heated while the refrigerant is cooled, thereby causing the refrigerant to condense. At the outside heat exchanger acting as an evaporator, a heat exchange takes place between the outside air and the refrigerant, so that heat is taken from the outside air while the refrigerant is heated, thereby causing the refrigerant to evaporate.
In such an air conditioning apparatus where the heating operation is carried out by the refrigerating cycle, a reduction in heating efficiency is inevitable when the temperature of the outside air is low, because the outside air is deprived of heat. Thus, a reduction in the outside air temperature will increase the work done by the compressor in maintaining a desired level of heating performance, which increases the electric power consumption of the motor. Furthermore, the increased work load of the compressor will increase the pressure of the refrigerant at the outlet of the compressor, thereby increasing the load of the compressor, which also increases the electric power consumption of the motor.